Knowledge Bank

There is considerable experimental and theoretical interest in the determination of the optical constants of aqueous solutions of sulfuric acid at various concentrations and temperatures. The presence of sulfuric acid droplets in the atmosphere of of Earth and $Venus1,2$ has been suggested and the scattered solar infrared radiation from atmospheric cloud droplets can be calculated from Mie theory provided that the relevant optical constants of sulfuric acid solutions are known. Previous $measurements3$ of the reflectance at near normal incidence and of the Lambert absorption coefficient of sulfuric acid solutions at $300\circ K$ have resulted in determination of the optical constants N = n + ik for several concentrations ranging from nearly pure water to nearly pure sulfuric acid. At the present time these studies are being extended to include experimental measurements for 75 and 96 percent by weight solutions of sulfuric acid at $250\circ K$, which is the temperature of the Venus cloud layer. The results of the analysis of the present reflectance measurements at near normal incidence will be presented and compared with previous Laboratory and planetary $studies.4,5$